July 4 - Terry Nichols will be back in a Denver courtroom this week to make a bold plea for a new trial on charges that he took part in the 1995 Oklahoma City bombing.

Nichols, serving a life sentence, already has had his conviction upheld by the U.S. 10th Circuit Court of Appeals.

But now he's claiming that the FBI improperly withheld from him thousands of so-called "lead sheets'' that would have strongly supported his innocence.

Some legal experts say Nichols, 44, has a reasonable chance of success.

Larry Pozner, a Denver lawyer who is president of the National Association of Defense Lawyers, said not turning over the lead sheets to the defense was "a major error'' by government prosecutors and the Federal Bureau of Investigation.

"The FBI has managed to shoot itself in the foot - and maybe in the heart,'' Pozner said. "I think it may well result in a new trial. ... They sat on evidence that points to Terry Nichols' innocence. Hiding evidence that points to innocence is the ultimate sin.''

The government, however, scoffs at Nichols' contention that he had no part in the bomb plot.

Prosecutors maintain that Nichols and co-defendant Timothy McVeigh bombed the Murrah Building to avenge the deaths of the Branch Davidians near Waco, Texas, two years earlier.

Prosecutor Sean Connelly, who is handling the appeal before U.S. District Judge Richard Matsch, said in court documents that the government was not required to hand over the lead sheets. They contain "early and speculative leads,'' Connelly argues, and the U.S. Supreme Court does not require prosecutors to turn such information over to the defense.

The lead sheets are summaries of the massive number of tips that poured into the FBI after the deadly April 19, 1995, bombing of the Alfred P. Murrah Federal Building, which killed 168 people and wounded more than 500 others.

Nichols' attorney, Michael Tigar, claims the lead sheets contain a wealth of exculpatory evidence that casts doubt on Nichols' guilt. For instance, Tigar says they show that McVeigh plotted the bombing not with Nichols but with a group of shadowy associates operating around Kingman, Ariz.

"The government put in issue Mr. Nichols alleged political beliefs, theorizing that Mr. Nichols and Mr. McVeigh formed a kind of political unit to carry out the bombing,'' Tigar recently wrote Matsch, who presided over the Nichols trial. "Now it turns out that Mr. McVeigh was in fact associated with a different political unit, based in Kingman. ... Mr. Nichols could not have been a part of this unit.''

Tigar said that as McVeigh plotted the bombing, he developed connections with various Arizona militia groups, tried to recruit Kingman residents into the plot and bought one of the key ingredients for the truck bomb - racing fuel - in Kingman.

Tigar also claimed the lead sheets showed that McVeigh's primary co-conspirator was an unidentified man known only as "John Doe No. 2.'' The two reportedly were seen together in Kingman, Ariz., and Junction City, Kan., where they allegedly rented the truck used in the bombing. Nichols, who will be in court Wednesday, will also ask for a new trial on one more ground.

He says that Roger Moore - an Arkansas gun collector who knew McVeigh and who authorities claim Nichols robbed - has changed his testimony.

The change, according to Tigar, was outlined in a letter Moore sent to Matsch last November.

At Nichols' trial, Moore testified that a masked intruder robbed him of dozens of guns, money and precious metals at his home in November 1994. Testimony by others tied the robbery to Nichols.

But Moore's account of the robbery in his letter to Matsch "differs in significant detail from ... trial testimony,'' said Tigar.

But the government says the evidence of Nichols' guilt is overwhelming.

Prosecutors say ammonium nitrate fertilizer used in the bomb was purchased by Nichols in September and October 1994 in Kansas. A month later, they say, Nichols robbed Moore in an attempt to bankroll the terrorist plot.

Prosecutors say a prepaid telephone calling card used by McVeigh and Nichols conclusively links the two men and shows the two used the card to call race tracks, heavy demolition companies and barrel-manufacturing companies in at attempt to obtain components for a truck bomb. The day before the deadly blast, McVeigh and Nichols assembled the bomb at Geary Lake State Park near Junction City, the government maintains.

On Feb. 26, the Denver-based 10th U.S. Circuit Court of Appeals, citing the "malicious nature of Mr. Nichols' conduct,'' upheld Nichols' conspiracy and involuntary manslaughter convictions and his sentence to life in prison and fine of $14.5 million.

After the trial, prosecutors admitted having "well over'' 40,000 lead sheets, including 18,000 from people who thought they saw two men initially believed to be suspects and identified as "John Doe No. 1'' and "John Doe No. 2.''

The government maintains that "John Doe No. 1'' is McVeigh and that John Doe No. 2 doesn't exist. Federal investigators believe that "John Doe No. 2'' existed only in the faulty memory of a witness at the Junction City shop where McVeigh rented the Ryder truck.

But the government contends that even if there was a broader conspiracy, the evidence is overwhelming that Terry Nichols is guilty of conspiring to blow up the Murrah Building.